Method of making ceramic electrical device

ABSTRACT

A METHOD OF MAKING A CERAMIC LIGHT BULB OR OTHER ELECTRICAL DEVICE HAVING A CERAMIC ENVELOPE PORTION FORMED OF A TRANSLUCENT CERAMIC MATERIAL AND A METAL CLOSURE MEMBER. THE CERAMIC MATERIAL IS METALIZED IN DESIRED AREAS. THE METAL CLOSURE MEMBER IS ASSEMBLED WITH THE CERAMIC ENVELOPE AND A FILAMENT IS MOUNTED WITHIN THE ENVELOPE WITH OPPOSITE ENDS IN CONTACT WITH METALIZED PORTIONS OF THE ENVELOPE. BRAZING METAL IS PLACED AT ALL CONTACT AREAS BETWEEN THE ENVELOPE AND THE CLOSURE MEMBER. THE ASSEMBLY IS THEN HEATED IN A FURNACE AT A TEMPERATURE AND TIME SUFFICIENT TO BRAZE THE ASSEMBLY INTO AN HERMETICALLY SEALED DEVICE.

R. A. KREY 3,701,578

METHOD OF MAKING CERAMIC ELECTRICAL DEVICE Oct. 31, 1972 Original FiledFeb. 28, 1966 United States Patent Patented Oct. 31, 1972 ABSTRACT OFTHE DISCLOSURE A method of making a ceramic light bulb or otherelectrical device having a ceramic envelope portion formed of atranslucent ceramic material and a metal closure member. The ceramicmaterial is metalized in desired areas. The metal closure member isassembled with the ceramic envelope and a filament is mounted within theenvelope with opposite ends in contact with metalized portions of theenvelope. Brazing metal is placed at all contact areas between theenvelope and the closure member. The assembly is then heated in afurnace at a temperature and time suificient to braze the assembly intoan hermetically sealed device.

BACKGROUND OF THE INVENTION This invention is a division of applicationSer. No. 530,- 716, filed Feb. 28, 1966, and now abandoned for CeramicLight Bulb with Metal Closure Member.

This invention relates to light bulbs of the incandescent type, and,more particularly, to a ceramic light bulb.

As is well known to those skilled in the lamp art, there is a constantsearch for light bulbs, particularly of the incandescent type, of astrong and rugged construction which will withstand abuse in handlingand shock and vibration during use. It has also become a recent desireto provide light bulbs of very small size for use in many types ofmodern electronic devices. Small light bulbs are necessary to provideillumination of various dials and the like as Well as provide necessaryindicator lights. Recent attempts at such light bulbs have resulted insmall glass light bulbs such as is shown and described in Pat. No.3,040,204. However, one problem with the light bulb disclosed therein isthe use of a glass envelope which is a fragile, low temperaturematerial. Also, the method of making such a light bulb is time consumingand expensive. As is well understood, it is desirable that light bulbsbe made as simple and as economical as possible.

It has recently been discovered that simple, economical, and very ruggedlight bulbs can be made from translucent, ceramic material. Such lightbulbs are very strong and can be made with very few parts. Also, it hasbeen discovered that light bulbs made of ceramic material may be madewith mounting means constructed as part of the light bulb, thuseliminating the necessity of separate mounting means.

It is therefore one object of this invention to provide a ceramic lightbulb of simple and rugged construction.

It is a further object of this invention to provide a ceramic light bulbwhich is small and compact and which may be mounted in any desiredlocation.

A further object of this invention is to provide a method of making aceramic light bulb.

A still further object of this invention is to provide a ceramic lightbulb without separate mounting means which may be mounted on any surfacesuch as a panel, for use as an indicator or illumination light.

SUMMARY OF THE INVENTION In carrying out this invention, in one form aceramic light bulb is provided which comprises a ceramic envelopeportion formed of any desired translucent ceramic material. A metallicclosure means is provided and is brazed to metalized portions of theceramic envelope. A filament is mounted within the ceramic envelope andhas its ends electrically connected in electrically isolated brazingmaterial. The ceramic light may be mounted by the metallic closuremember. The metallic closure member and a portion of the ceramicenvelope at the brazing material provide electrical connections to theopposite ends of the filament.

The ceramic light bulb is made in a preferred form by metalizing ceramicmaterial used to form the light envelope. The, thin film of metal formedby metalizing is ground off of the ceramic material, as necessary, inthe areas where translucency is desired and in those other areas whereelectrical insulation is desired. A metal closure member is assembledwith the ceramic envelope and a filament is mounted within the ceramicenvelope with its opposite ends in contact with metalized portions ofthe envelope which are electrically isolated from each other. Brazingmetal is placed at all contact areas of the ceramic envelope, thefilament and the metal closure member. The assembly is then heated in afurnace, in an atmosphere of hydrogen at a temperature and for a timesufficient to braze the assembly into an hermetically sealed light. Thelight is then heated in a vacuum at approximately 700 C. forapproximately ten minutes to remove the hydrogen by diffusion throughthe hot metal closure member.

The invention which is sought to be protected will be clearly pointedout and distinctly claimed in the claims appended hereto. However, it isbelieved that this invention, and the manner in which its variousobjects and advantages, as well as other objects and advantages, areobtained will be more fully understood by reference to the followingdetailed description of preferred embodiments thereof, particularly whenconsidered in the light of the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a perspective view of a ceramiclight bulb according to a preferred embodiment of this invention;

FIG. 2 is a sectional view of the ceramic light bulb shown in FIG. 1;

FIG. 3 is a sectional view similar to FIG. 2 showing another form of theceramic light bulb according to this invention; and

FIG. 4 is a sectional view of a ceramic light bulb, as shown in FIGS. 1and 2, showing a preferred method of construction.

DESCRIPTION OF PREFERRED EMBODIMENTS While the following descriptionwill set forth a preferred ceramic light bulb and a preferred method ofmaking such bulb, according to the embodiments of the inventiondisclosed in the drawing, it will be understood that such description isfor illustrative purposes only and should not be considered as limitingthe scope of the invention.

Reference will now be made to the drawing, in which like parts will beindicated by like numerals throughout the various views thereof.Referring first to FIG. 1, there is shown a ceramic light bulb 10 madeaccording to the present preferred embodiment of this invention. Asshown, ceramic light bulb 10 comprises a ceramic envelope portion formedof ceramic members 12 and 14. 14 is the base member, as clearly shown inFIG. 2. The ceramic envelope portion of bulb 10 is sealed by a metallicclosure member 16. As will be apparent from FIG. 1, the ceramic lightbulb will provide illumination, particularly through ceramic member 12when filament 18 (FIG. 2) is heated by electric current.

Considering FIG. 2 of the drawing, it can be seen that the ceramicenvelope portion, comprising ceramic members 12 and 14, is metalized toprovide the thin metallic films or layers indicated at 20, 22 and 24. Aswill be understood, the ceramic members 12 and 14 may be made of anydesired translucent ceramic material. Alumina and forsterite are twoexamples of translucent ceramic which may be used in this invention. Theceramic members. may be metalized in any known manner. One method ofmetalizing, which is described in Pat. No. 2,647,218 for CeramicElectron Tubes, uses finely divided molybdenum powder, which is coatedon the ceramic. The coated ceramic is then fired in hydrogen to atemperature of approximately 1500 C. This sinters the metal powder tothe ceramic surface, producing a thin metallic layer which is firmlybonded to the surface of the ceramic. Another method of metalizing isshown and described in Pat. No. 3,215,555 issued in the name of thepresent inventor. Of course, any other method of metalizing may be used.In the preferred form of this invention the molybdenum film is platedwith nickel to aid the flow of the brazing metal during the brazingoperation, as will be more fully described hereafter.

Referring again to FIG. 2, ceramic member 12 may be metalized only alongthe rim 26, as is indicated by metal film 20. The base member 14 isprovided with a dished portion 28 and a hole 30 extending through to thedished portion 28, as shown. Ceramic member 14 will be metalized on bothsides to provide the metal film 24 in both the dished portion 28 and inthe hole 30, as shown. The metal film 22 is also formed around the edgeof base member 14. After base member 14 has been metalized, the upperand lower surface will be ground to remove the metal film from thesesurfaces while leaving it in the dished portion 28, the hole 30 and theedge. The grinding will isolate electrically the metal film 24 in dishedportion 28 and hole 30 from the metal film 22 at the edge of ceramicbase member 14. The flanged metal closure member 16 is cylindrical inshape, having an upper edge 32 and a flange 34 on its lower end. Asshown, cylindrical member 16 is sized such that the upper edge 32 willmate with the rim 26 of the upper ceramic member 12. Also, lower ceramicmember 14 will fit snugly within the lower portion of closure member 16,as shown. The metal closure memher is preferably made of metal whichwill have the same thermal expansion as the ceramic material. When theceramic material is forsterite a 52% nickel iron metal may be used.Metal such as kovar may be used with alumina.

The bulb is assembled by brazing the metal closure member 16 to theceramic envelope portion. The upper member 12 of the envelope is brazedto edge 32, as shown using any desired brazing metal. The brazing metalwill firmly adhere the metal film on rim 26 to the upper edge 32. Thelower, base portion 14 of the envelope is brazed to the lower end of thecylindrical closure member 16, the brazing metal making a firm bondbetween the metal closure member 16 and the metal film 22 on the edge ofbase member 14. As will be understood, the brazing of closure member 16to the ceramic envelope portion will form an hermetic seal between thesemembers, providing an hermetically sealed bulb 10. The filament member18 is mounted within bulb member 10, having one end electricallyconnected to the brazing metal between edge 32 and rim 26. The oppositeend of filament 18 is mounted in hole and is brazed to the metal film 24during the brazing operation. If desired, a lead wire, indicated at 19may be attached to the inner end of filament 18, such lead wire beingbrazed to metal film 24. Thus, the bulb 10 is provided with contactsformed by flange 34 of metal closure member 16 and the metal film 24 indished portion 28 of the lower member 14 of the envelope. As will beapparent from FIGS. 1 and 2, the bulb 4 10 may be mounted by means offlange 34 to any desired surface. The light from bulb 10 will diffusethrough the ceramic envelope, formed by ceramic members 12 and 14.

FIG. 3 shows another embodiment of the ceramic bulb of this invention.In the embodiment of FIG. 3, a ceramic bulb 10 is shown, provided with aceramic envelope portion composed of ceramic members 42 and 44. Ceramicmember 42 is in the form of a circular cap member having a depressed rim46, as shown. Ceramic member 44 is in the form of a cylindrical member.Depressed rim 46 and upper and lower rims or edges 48 of cylindricalmember 44 are metalized to provide the metal films 50 on rim 46 and 52on edges 48.; Also edge 54 of cap member 42 is metalized to provide themetal film 56. A metal closure member 58 is provided, brazed to thelower edge 48 of ceramic cylinder 44, as shown. As will be understood,cap member 42 is also brazed to the upper edge 48 of cylinder 44,thereby forming an hermetically sealed bulb 10'. Filament member 60 ismounted diagonally across ceramic cylinder 44, with its opposite endselectrically connected to the brazing metal in the sealed areas betweenceramic cap 42 and the cylinder 44 at one end and the closure member 58and the cylinder 44 at the other end. As will be apparent from FIG. 3bulb 10' may be mounted by metal base member 58, with the electricalconnections made between the base metal closure member 58 and the metalfilm 56 on the ceramic cap 42. If desired, ceramic part 42 could be ofsmaller diameter, leaving a ledge on the upper edge 48 of ceramic member44, thereby providing a contact to metal film 52.

FIG. 4 shows a preferred manner of making the ceramic bulb of thisinvention. The embodiment shown in FIG. 4 is the same as that shown inFIGS. 1 and 2. As shown in FIG. 4, the ceramic envelope is formed of twopieces of ceramic material 12 and 14, both being approximately 50 milsthick. Metal closure member 16 is formed from a compatible metalapproximately 10 mils thick. As earlier noted, when the ceramic materialof parts 12 and 14 is forsterite then metal member 16 is desirablyformed of 52% nickel iron. Filament member 18 is formed of approximately0.5 mil tungsten. Ceramic parts 12 and 14 of the envelope are metalized,for example with molybdenum and then coated with nickel. The parts arethen ground, as necessary, to leave metal film 20 on rim 26 of part 12,and film 22 on the edge of part 14, with film 24 in dished portion 28and hole 30. The base member 14 is placed within the lower end of metalclosure member 16 and a ring of brazing metal, for example copper, isplaced on top of the base member 14 against the inner surface of metalclosure member 16. The filament member 18 is then mounted with one endsecured to a lead in wire 19, which is mounted within hole 30 in contactwith metal film 24. The other end of filament 18 rests on the upper edge32 of closure member 16. A brazing ring 72 is placed around the end ofthe lead wire 19 within the hole 30, as shown. In the preferred form ofthis invention, lead wire 19 is formed of molybdenum, approximately 15mils in diameter. The hole 30 is approximately 17 mils in diameter.However, it should be understood that lead wire 19 may be omitted andthe end of filament 18 brazed to metal film 24 in hole 30. Anotherbrazing ring 74 is placed on top of flange 32. This ring 74 ispreferably made from 3 mil flat stock. In place of brazing ring 74, a 3mil coat of copper, or other brazing material may be coated on metalfilm 20. Then the upper ceramic member 12 is placed on top of thebrazing ring 74. If desired, a molybdenum clamp 76 may be used to clampthe assembly together, as is shown. Alternatively, a clamping fixturemay be provided. The clamped assembly is then placed in a furnace,preferably in an atmosphere of hydrogen, and heated to a temperaturesufficient to melt the brazing metal and braze the part together. Thiswill form an hermetically sealed light bulb 10. The assembly may then beplaced in a vacuum oven and heated to a temperature of approximately 700C. for approximately ten minutes to evacuate the sealed bulb bydiffusing the hydrogen out through the heated metal, which is porous tohydrogen when heated.

From the above description, it will be apparent to those skilled in thelamp art that there has been provided a novel ceramic light bulb.Obviously, the light bulb of this invention will be rugged and capableof being manufactured in very small sizes at low costs. If desired,support members may be provided for the filament as is well understoodin this art. Such supports could be brazed to isolated metal films onone of the ceramic members.

While there have been shown and described the present preferredembodiments of this invention, and the preferred method of manufacture,it will be clear that many changes may be made in the various describedconstructions without departing from the scope of this invention, as setforth in the appended claims.

What is claimed as new and which it is desired to secure by LettersPatent of the United States is:

1. A method of making a ceramic light bulb comprising the steps of;metalizing ceramic material forming an envelope to form a metal filmthereon, grinding said metalized ceramic material envelope to removesaid metal film from desired translucent areas and to electricallyisolate portions of said film, assembling a metal closure member withsaid ceramic envelope, mounting a filament member within said envelopeand in electrical contact with electrically isolated portions of saidmetal film, placing brazing metal at all contact areas, brazing saidassembly in a furnace with a hydrogen atmosphere, and then heating saidbrazed assembly in a vacuum oven at a temperature of approximately 700C. for approximate- 1y ten minutes to evacuate the hydrogen from saidassembly by diflfusing it through the heated metal.

2. A method of making an hermetically sealed electrical ceramic devicecomprising the steps of; forming a ceramic envelope; metalizing portionsof said ceramic envelope forming electrically isolated areas of metalfilm thereon; assembling a metal closure member with said ceramicenvelope; mounting an electrical member within said envelope and inelectrical contact with said isolated film areas; placing brazing metalat all contact areas; and brazing said assembly to seal said assembly.

3. A method of making an hermetically sealed electrical ceramic deviceas claimed in claim 2 in which the brazing step is carried out in ahydrogen atmosphere and then heating said brazed assembly in a vacuumoven at a temperature of approximately 700 C. for approximately 10minutes to evacuate the hydrogen from said assembly by diffusion throughthe heated metal.

References Cited UNITED STATES PATENTS 573,088 12/1896 Hawkins 313-315 X2,245,782 6/1941 Holloway 313-315 X 2,393,711 11/1946 Schwarze 431-932,427,711 9/1947 Cartun 313-318 X 2,719,185 9/1955 Sorg et al. 313-317 X3,020,437 2/1962 Horan 313-318 3,065,291 11/1962 Rexer, Jr. 313-318 X3,243,635 3/ 1966 Louden 313-317 2,296,575 9/ 1942 Rowley et al 29-5832,810,283 10/1957 Cohen et a1 313-318 3,149,396 9/1964 Warren 29473.1 X3,188,512 6/1965 Moore 313-315 X 3,302,961 2/ 1967 Franklin 29-473.1 X3,386,011 5/1968 Murray, Jr., et al. 29-583 X 3,576,066 4/1971 Stewardet al. 316-18 OTHER REFERENCES R.C.A. Technical Notes, No. 610, March1965, Detailed Description Ceramic or Ceramic Metal Lamps by Roger A.Krey.

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US.Cl. X.R.

